1. Field of the Invention
The subject invention relates to a new, useful and improved process for the formation of fibrils from very high molecular weight polymers. More particularly, the present invention pertains to an improved method for making fibrils from olefin polymers, polyethylene and polypropylene in particular, which are especially suitable for and adaptable to incorporation into paper or other sheet-like structures by the papermaking process. In this respect, the invention also pertains to the improved synthetic fibrils produced or made in accordance with the process of this invention.
One of the main applications of the fibrils produced in accordance with this invention and by the method of the invention is that application based on their ability to form coherent self-supporting water leaves which can be used for making sheet-like structures according to the methods and processes of paper manufacturing.
2. Description of the Prior Art
Numerous efforts have been made to transform man-made polymers and fibers produced therefrom into structures which are similar to natural cellulosic paper, and which possess in the wet state sufficient coherence to enable them to be processed on conventional paper-making machines. However, most of these efforts have not been successful. This is particularly true with the olefin polymers such as polyethylene and polypropylene, due to the fact that fibers of both of these materials are hydrophobic, do not readily hydrate or fibrillate, and cannot be converted into self-bonding webs on paper-making machinery (see Page 51 of the paper entitled "Wet Formation with Synthetic Organic Polymers" by H. Mark presented at the sumposium on "Consolidation of the Paper Web", Cambridge, Sept. 1965). These failures may in part be due to the fact that, unlike natural cellulosic fibers, man-made fibers prepared according to ordinary production methods are usually not fibrillated when beaten in water, but only disintegrate into small chips.
Numerous special processes have been proposed for preparing polymer fibrils having characteristics rendering them suitable for use in paper-making processes. Included among such processes are those described in U.S. Pat. Nos. 2,999,788 and 2,988,782. These patents describe a process in which a polymer is dissolved in a solvent and added to a liquid having essentially no solvent power for the polymer. A high level of agitation is provided as the polymer solution is added to the non-solvent liquid so that polymer solution is subjected to shearing forces to attenuate the droplets of polymer solution into fine streams to thereby orient the solute polymer molecules. The non-solvent liquid diffuses into the polymer solution and precipitates the polymer therefrom in the form of fine fibrils.